Drive systems with internal combustion engine and expander coupled with the same are known from the prior art and are to be increasingly employed also in the field of a mobile application such as for example a motor vehicle. Since for driving the expander a combustible working medium is often employed, which is optimal both ecologically and also economically, a particularly good sealing of the individual components, in particular in the region of a shaft passage to the internal combustion engine or into the surroundings has to be ensured.